emitted by Zinc bombarded by Alpha Rays. 



493 



lower end a small plate of zinc X with a projecting piece S 

 which came into contact with the cup C when the rod H 

 was raised by the windlass. A slender brass rod connected 



the 



cup 



to a sensitive electrometer. P was a circulai 

 Fig. 1. 



Electrcmetz- c 



plate of copper 2 cm. in diameter, with a deposit of polonium 

 on its anterior face. As shown in the figure it could be 

 connected as desired to either terminal of a battery of small 

 storage-cells. The tube B' was filled with coconut charcoal 

 which was used for the purpose of improving the vacuum 

 made with a Gaede rotary mercury-pump. F was a small 

 fused quartz furnace-tube and was provided with platinum 

 heating-coils as shown. It was held in an upright position 

 by means of a short glass rod sealed into the base of the 

 heating-chamber. When making zinc deposits on the 

 surface of the zinc plate X the apparatus was first of all 

 evacuated as highly as possible with the Gaede pump in 



